Are you sure you have the correct resistor numbers there? It would be really shocking if those resistors were toasted. Maybe post a picture of the toasted resistors. Maybe they are just dirty?

https://www.ipdb.org/files/317/Williams_1980_Blackout_Schematics_pages_numbered_7_through_22.pdf

The resistors are listed at the bottom of the table on page 4

Row 4 appears to be locked on. Check IC19, Q52 and Q53 to make sure there isn't solder splash on them. Check the legs of Q52 to make sure they didn't get twisted and are touching. Diode check Q52 and Q53 and compare to the others in the area. Check R116 to make sure it is still soldered in place properly.

Those resistors get very hot and is why your board is scorched in that area (common with games of this era with lots of hours). If you want to eliminate the heat there, you can replace the transistors in the lamp matrix with MOSFETS.

Did this problem start before or after you replaced the header pins on J7? Can you inspect those header pins (particularly pin 4) for shorted pins, large solder blobs that might be contacting the mounting bracket in the backbox. Make sure you have the CPU and driver boards physically installed properly.

That is the mystery. Nothing comes to mind that you could do to the switch matrix that could cause a problem with the lamp matrix. The circuits are very un-related.

I noticed the AMI PIAs too.

Seems like a really odd coincidence that the PIA would give up the ghost at this exact moment, but that could be it.

Maybe take the board set to your friend that tested them out originally and ask him to see why Row 4 of the lamp matrix is locked on.

Do not replace the PIA. All your feature lamps are working properly so the PIA is fine.

Are all the 100s and 1000s digits out on all the displays or just player 1? If it's just player 1, swap the displays between player 1 and say player 4 to see if the problem follows the display. It looks like your display may be outgassed (worn out) but if all your displays are doing the same or if the display works fine in another position, the problem is likely on the master board or connections somewhere.

Please measure the power supply voltage to the displays. Power Board connector J5 (upper far left 6 pin connector). The left-most pin is Pin 1

Meter on DC - black lead to ground.

Pin 1 : 0V (ground)
Pin 2 : not used
Pin 3 : -100V
Pin 4 : +100V
Pin 5 : Key (not used)
Pin 6 : 5V

Be careful, this is high voltage stuff.

If you modded the power supply then both the positive and negative supplies should be reduced to 91ish. Did you replace both ZR2 and ZR4 with 91V zeners?

ZR1 on the MDB reduces the 100V supply an additional 10V. So in essence the circuit is seeing +80V and -100V which is a spread of 20V as opposed to the normal 10V. I know later plasma DMDs have troubles if their supply voltages are out of spec. Wonder if a similar situation applies to earlier numeric display?

Can you put the 100V zener back in the positive 100v power supply or lower the -100 supply by installing a 91V zener?

Which one, there are 2 of them?

One drives the MDB display and players 1 and 2 and the other players 3 and 4? If the displays are exhibiting the same problem no matter which position they are connected, its very unlikely that both these chips failed in the same way.

Can you connect one of your displays to the player 3 or 4 cable and double check it they both still have the same problem? That will help narrow this down.

In any event, you should reflow the solder to the suspect chip before replacing it. Heat related changes can be caused by cold solder joints.

IC5 is very close to that connector. It is possible you are heating it up just as much as the connector. IC5 is the BCD decoder for P1, P2 and Master. Maybe reflow solder to IC5. Of course, IC5 would only be the problem if the condition is limited to P1, P2 and the master and P3 and P4 work perfectly.

IC18 could be your display issue just as much as IC6 could be it.

Not sure how IC18 (6821) would effect your lamp matrix issue unless it is corrupting the data bus or something. Can you or someone explain the thought process there?

Holy cow that game is in great shape! I've never seen the brass parts that clean and shiny as well as the cleanliness of the cabinet.